Heat sink adapted for dissipating heat from a semiconductor device

ABSTRACT

A heat sink adapted for dissipating heat from a semiconductor device. The heat sink has lower heat sink body, an upper heat sink body soldered to the lower heat sink body, an airtight chamber defined in between the upper heat sink body and the lower heat sink body and drawn into a vacuum status, a working fluid filled in the airtight chamber for circulation between gas phase and liquid phase to transfer heat energy from the bottom side of the heat sink toward the top side thereof, and a porous structure formed in the upper heat sink body and the lower heat sink body inside the airtight chamber for accelerating the circulation of the working fluid between gas phase and liquid phase.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor device cooling structure and, more specifically, to a heat sink adapted for dissipating heat from a semiconductor device, for example, a CPU or the like efficiently. The heat sink uses a working fluid and a porous structure to improve heat dissipation efficiency by means of the change of the working fluid between gas state and liquid state.

[0003] 2. Description of the Related Art

[0004]FIG. 1 illustrates a prior art heat sink 10 used with a fan 11 for dissipation of heat energy from an electronic device, for example, a CPU 14. The heat sink 10 is made of copper or aluminum, comprising a metal base 12 extruded from copper or aluminum and radiation fins 13 upwardly extended from the top sidewall of the metal base 12. During running of the CPU 14, the base 12 transfers heat energy from the CPU 14 to the radiation fins 13, and the fan 11 causes currents of air toward the radiation fins 13 to carry heat energy away from the radiation fins 13, so as to reduce the working temperature of the CPU 14 and extend its service life. However, following fast development of electronic devices of high operational speed, advanced electronic devices produce much heat energy when working. Because advanced electronic devices are made smaller and smaller, the heat energy produced by an advanced electronic device during its operation is centralized (the so-called hot point). In order to rapidly effectively dissipate heat from an electronic device, a relatively greater heat dissipation device area and/or a relatively bigger scale of fan may be used. However, the use of a big heat dissipation device and a big scale of fan greatly increases the dimensions, weight, and manufacturing cost of the electronic device. Further, the operation of a big scale of fan produces much noise. There are also known heat dissipation devices using a heat exchanging technology based on the application of gas-liquid phase change to dissipate heat energy. A heat dissipation device based on this technology requires a hollow metal base filled with a working fluid that can be changed between gas phase and liquid phase. When attached to an electronic device, the hollow metal base transfers heat energy from the electronic device to the working fluid, thereby causing the working fluid to be vaporized. The steam thus produced makes a heat exchange with the outside cooling air, so that the working temperature of the electronic device is quickly reduced. The heat dissipation efficiency of the hollow metal base is still not as high as expected. Further, the hollow metal base is comprised of an upper half and a lower half welded together. Because the peripheral bottom edge of the upper half and the peripheral top edge of the lower half are flat edges, it is difficult to solder a solder to the peripheral bottom edge of the upper half and the peripheral top edge of the lower half. This soldering problem results in low yielding rate during a mass production.

SUMMARY OF THE INVENTION

[0005] The present invention has been accomplished to provide a heat sink, which eliminates the aforesaid drawback. It is the main object of the present invention to provide a heat sink, which uses a working fluid to improve heat dissipation efficiency by means of the circulation between gas phase and liquid phase. According to w one aspect of the present invention, the heat sink comprises an upper heat sink body, a lower heat sink body soldered to the upper heat sink body, an airtight chamber defined in between the upper heat sink body and the lower heat sink body, a working fluid filled in the airtight chamber for circulation between gas phase and liquid phase to transfer heat energy from the bottom side of the heat sink toward the top side thereof, and a porous structure formed in the upper heat sink body and the lower heat sink body inside the airtight chamber for accelerating the circulation of the working fluid between gas phase and liquid phase. According to another aspect of the present invention, a gap is left between the periphery of the upper heat sink body and the peripheral wall of the lower heat sink body for the positioning of a solder, which is further melted to fixedly fasten the upper heat sink body to the lower heat sink body, keeping the inside space of the lower heat sink body in an airtight status. According to still another aspect of the present invention, the airtight chamber is maintained in a vacuum status so that the working fluid can quickly be vaporized during transferring of heat energy from the semiconductor device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a sectional view showing a heat sink used with a fan and attached to a CPU according to the prior art.

[0007]FIG. 2 is an elevational view of a heat sink constructed according to the present invention.

[0008]FIG. 3 is a schematic drawing showing the construction of the heat sink according to the present invention.

[0009]FIG. 4 is a sectional view of the present invention showing the molten solder filled up the groove in between the peripheral wall of the lower heat sink body and the periphery of the upper heat sink body.

[0010]FIG. 5 is an elevational view of an alternate form of the heat sink according to the present invention.

[0011]FIG. 6 is a schematic drawing showing another alternate form of the heat sink used with a fan according to the present invention.

[0012]FIG. 7 is a sectional view of still another alternate form of the present invention before melding of the solder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] Referring to FIGS. 2, and 3, the heat sink, referenced by 20, is made of metallic material of high coefficient of heat transfer (silver, copper, aluminum, or their alloy), comprised of an upper heat sink body 22 and a lower heat sink body 21. The upper heat sink body 22 and the lower heat sink body 21 are fixedly fastened together, defining an airtight chamber. Further, the heat sink 20 has a heat receiving face 212 closely attached to a semiconductor device, for example, a CPU 14 to receive heat from the CPU 14, for enabling heat energy to be further dissipated into the air through the top sidewall of the upper heat sink body 22. The airtight chamber defined in the heat sink 20 between the lower heat sink body 21 and the upper heat sink body 22 has a porous structure 24 on the inside, and a working fluid 23 filled therein. The porous structure 24 is formed by: sintering metal powder (copper powder, nickel powder, silver powder, or their mixture) to the inside wall of the airtight chamber of the heat sink 20, or coarsening the inside wall of the airtight chamber of the heat sink 20. The porous structure 24 greatly increases heat transfer area, and can absorb steam from boiling working fluid, by means of capillary effect, to accelerate the circulation of fluid-gas phase exchange of the working fluid 23.

[0014] If the aforesaid porous structure 24 is formed by sintering metal powder to the inside wall of the airtight chamber of the heat sink 20, the radius of the metal powder can be determined subject to the following equation:

r _(c)=(4σ/Δρ)cos γ/2   1.

[0015] (r_(c): radius of capillary; σ: surface tension coefficient; ρ: pressure drop; γ: wetting angle)

r=r _(c) /c   2.

[0016] (c: constant determined subject to the shape of metal powder, normally 0.41) (r: radius of powder)

[0017] Further, the porous structure 24 in the lower heat sink body 21 rapidly evenly transfers heat energy from the CPU 14 to the working fluid 23, thereby causing the working fluid 23 to be quickly evaporated. The thickness of the porous structure 24 is about 2˜10 times of the radius of powder. The filling amount of the working fluid 23 is within 0.5˜2 times of the total space of the pores of the porous structure 24. The working fluid 23 can be obtained from water, alcohol, acetone, or any of a variety of cooling agent that has high latent heat and low boiling point. The porous structure 24 greatly increases heat dissipation area, and accelerates heat change action. By means of capillary effect, the porous structure 24 absorbs vaporized working fluid and then condenses vaporized working fluid into fluid state.

[0018] The lower heat sink body 21 comprises an obliquely outwardly extended peripheral wall 211. Further, the upper heat sink body 22 and the lower heat sink body 21 have respective supports 27. The upper heat sink body 22 is attached to the lower heat sink body 21 and supported on the inner surface of the peripheral wall 211 of the lower heat sink body 21 near the topmost edge of the peripheral wall 211, keeping the supports 27 of the upper heat sink body 21 stopped against the supports 27 of the lower heat sink body 21, and then the upper heat sink body 22 is soldered to the peripheral wall 211 of the lower heat sink body 21. The aforesaid porous structure 24 can also be formed in the supports 27. During running of the CPU 14, the heat receiving face 212 absorbs heat energy from the CPU 14, and transfers absorbed heat energy to the stop side of the upper heat sink body 22. Alternatively, the supports 27 can be formed of porous material. It is not necessary to have the porous structure 24 evenly distributed over the supports 27, i.e., the porous structure 24 has a relatively higher density of pores in the area where the working fluid 23 can quickly be boiled.

[0019] When the upper heat sink body 22 and the lower heat sink body 21 closely attached together, a groove 26 is formed at the topside within the peripheral wall 211 of the lower heat sink body 21 around the periphery of the upper heat sink body 22 for the positioning of a solder 25. After positioning of the solder 25 in the groove 26, the upper heat sink body 22 and the lower heat sink body 21 are heated to melt the solder 25, thereby causing the upper heat sink body 22 to be fixedly fastened to the peripheral wall 211 of the lower heat sink body 21, keeping the inside space of the upper heat sink body 22 in an airtight condition. After connection of the upper heat sink body 22 to the lower heat sink body 21, the heat sink 20 is processed to form the desired porous structure 24. Because the sintering of metal powder in the airtight chamber of the heat sink 20 must be performed under a high temperature, an oxide may be produced from the metal powder or the heat sink 20 during sintering. In order to eliminate this problem, the sintering process is performed under a vacuum environment or the presence of a reduction gas (hydrogen) or inert gas (nitrogen or argon).

[0020] Referring to FIGS. 2 and 3 again, after bonding of the upper heat sink body 22 and the lower heat sink body 21, the working fluid 23 is filled in the airtight chamber of the heat sink 20, and air is then drawn away from the airtight chamber of the heat sink 20 through a suction tube 28, which is installed in the peripheral wall 211 of the lower heat sink body 21 at one side. After the airtight chamber of the heat sink 20 has been turned into a vacuum status, the suction tube 28 is cut off and sealed, keeping the outer surface of the peripheral wall 211 of the lower heat sink body 21 in a flush manner.

[0021]FIG. 4 shows an alternate form of the present invention. According to this embodiment, the supports of the heat sink bodies are not vertically aligned, i.e., the supports 27 of the upper heat sink body 22 are stopped at the top side of the bottom wall of the lower heat sink body 21, and the supports 27 of the lower heat sink body 21 are stopped at the bottom side of the upper heat sink body 22.

[0022]FIG. 5 shows another alternate form of the present invention. According to this embodiment, the heat sink 20 further comprises a substantially U-shaped circulation tube 29 protruded from one side of the peripheral wall 211 of the lower heat sink body 21. The circulation tube 29 has two distal ends respectively disposed in communication with the airtight chamber of the heat sink 20. When the working fluid vaporized, the steam of the working fluid passes to the inside of the circulation tube 29 to make a heat exchange with external cooling air. After dissipation of heat, the steam is condensed into fluid, which flows back to the inside of the airtight chamber in the heat sink 29. Further, a fan (not shown) may be provided above or below the circulation tube 29 to accelerate the condensing of the steam.

[0023] The rapid heat dissipation action of the heat sink 20 is described hereinafter. When installed, the heat receiving face 212 is disposed in close contact with the CPU 14. During running of the CPU 14, the heat receiving face 212 transfers heat energy from the CPU 14 to the working fluid 23, i.e., the so-called evaporation end, thereby causing the working fluid 23 to be evaporated. Because the inside space of the heat sink 20 is maintained in a vacuum status, the working fluid 23 can quickly be vaporized at a temperature lower than the boiling point of the working fluid 23 at the atmospheric pressure. The internal pressure of the heat sink 20 is within 100 torr˜1×10−3 torr. If water is used for the working fluid 23, the boiling point of the working fluid 23 is 100° C. under the pressure of 760 torr, or 40° C. under the pressure of 55torr. Therefore, lowering the internal pressure of the heat sink 20 relatively accelerates the vaporizing speed of the working fluid 23. When the working fluid 23 vaporized, the steam thus produced reaches the topside of the airtight chamber in the upper heat sink body 22 (see the hollow arrowhead signs in FIG. 3) to transfer heat energy to the upper heat sink body 22. When the steam reached the topside in the upper heat sink body 22, the porous structure 24 absorbs the steam by means of capillary effect, enabling heat energy to be quickly dissipated from the upper heat sink body 22 into the outside air. When heat energy transferred from the steam to the upper heat sink body 22, the steam is condensed into fluid, which flows downwards along the supports 27 to the bottom side of the airtight chamber in the lower heat sink body 21 (see the solid arrowhead signs in FIG. 3). By means of the circulation of gas phase-liquid phase change, heat energy is quickly carried away from the CPU 14.

[0024]FIG. 6 shows still another alternate form of the present invention. According to this embodiment, the heat sink 20 further comprises a radiation fin unit 30 soldered to the top sidewall of the upper heat sink body 22 with a solder 25, and adapted for supporting a fan 40.

[0025]FIG. 7 shows still another alternate form of the present invention. According to this embodiment, the heat sink 20 is comprised of an upper heat sink body 22 and a lower heat sink body 21. The lower heat sink body 21 comprises an upright peripheral wall 211. The upper heat sink body 22 is inserted into the lower heat sink body 21, having a flange 2211 outwardly extended from the downward peripheral wall 221 thereof. The lower heat sink body 21 and the upper heat sink body 22 have supports 27 supporting each other. After insertion of the upper heat sink body 22 into the lower heat sink body 21, a solder 25 is put on the outward flange 2211 of the upper heat sink body 22 within the upward peripheral wall 211 of the lower heat sink body 21. When the solder 25 melted, the molten solder flows into the groove 26 within the upward peripheral wall 211 of the lower heat sink body 21 around the outward flange 2211 of the upper heat sink body 21 to fixedly fasten the upper heat sink body 22 to the lower heat sink body 21.

[0026] In the aforesaid embodiments, the solder 25 can be a silver solder, a copper solder, a nickel solder, or a tin solder.

[0027] A prototype of heat sink has been constructed with the features of the annexed drawings of FIGS. 2˜6. The heat sink functions smoothly to provide all of the features discussed earlier.

[0028] Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims. 

What the invention claimed is:
 1. A heat sink comprising a lower heat sink body, said lower heat sink body having an upward peripheral wall, an upper heat sink body mounted in said lower heat sink body and fixedly fastened to the upward peripheral wall of said lower heat sink body, an airtight chamber defined in between said upper heat sink body and said lower heat sink body, a working fluid filled in said airtight chamber, a porous structure formed in said upper heat sink body and said lower heat sink body inside said airtight chamber, and a solder soldered to said upper heat sink body and the peripheral wall of said lower heat sink body.
 2. The heat sink as claimed in claim 1, wherein said upper heat sink body comprises a downward peripheral wall inserted into said lower heat sink body and spaced from the upward peripheral wall of said lower heat sink body at a distance within which said solder is inserted, the downward peripheral wall of said upper heat sink body having an outward bottom flange soldered to the upward peripheral wall of said lower heat sink body by said solder.
 3. The heat sink as claimed in claim 1, wherein said porous structure is formed of a metal powder in said upper heat sink body and said lower heat sink body by sintering under the presence of a reduction gas.
 4. The heat sink as claimed in claim 1, wherein said porous structure is formed of a metal powder in said upper heat sink body and said lower heat sink body by sintering under the presence of an inert gas.
 5. The heat sink as claimed in claim 3, wherein said metal powder is selected from copper powder, nickel powder, and silver powder, and their compound and alloy powder.
 6. The heat sink as claimed in claim 4, wherein said metal powder is selected from copper powder, nickel powder, and silver powder, and their compound/alloy powder.
 7. The heat sink as claimed in claim 1, wherein said porous structure has a thickness about 2˜10 times of the radius of powder of said metal power.
 8. The heat sink as claimed in claim 1, wherein said upper heat sink body and said lower heat sink body each have a coarsened inside wall forming said porous structure.
 9. The heat sink as claimed in claim 1, wherein the filling amount of said working fluid in said airtight chamber is about 0.5˜2 times of the total space of pores in said porous structure.
 10. The heat sink as claimed in claim 1, wherein said airtight chamber has a pressure within the range of 100 torr to 1×10−3 torr.
 11. The heat sink as claimed in claim 1 further comprising a suction tube disposed at one side in communication with said airtight chamber and adapted for drawing air out of said airtight chamber.
 12. The heat sink as claimed in claim 1 further comprising a circulation tube protruded from one side thereof, said circulation tube having two distal ends disposed in communication with said airtight chamber.
 13. The heat sink as claimed in claim 1, wherein said upper heat sink body and said lower heat sink body are made of metal material selected from copper, aluminum, and their alloys.
 14. The heat sink as claimed in claim 1, wherein said solder is silver solder.
 15. The heat sink as claimed in claim 1, wherein said solder is copper solder.
 16. The heat sink as claimed in claim 1, wherein said solder is nickel solder.
 17. The heat sink as claimed in claim 1, wherein said solder is tin solder. 